Ultrasonic imaging (or insonification of anatomical structures has come to the fore as a diagnostic technique within the last decade and is also now beginning to be used in monitoring a patient's condition during surgical and other procedures. In the insonification technique, ultrasonic energy is transmitted into a body; and this energy, as reflected from body fluids, organs, tissues, and other anatomical structures on which it impinges, is intercepted. The information contained in the intercepted energy is extracted and processed, providing an indication of the patient's condition. Insonification is commonly used to identify a wide range of physical conditions and/or disorders. For example, it is employed in prenatal examinations of a fetus, diagnosis of abnormalities of cardiac structures, and in the measurement of cardiac output.
It is to the latter application of ultrasonic instrumentation that the present invention is specifically directed. In that application, as envisaged by us, the ascending aorta of the patient is insonified with ultrasonic energy propagated from an ultrasonic energy transmitting transducer probe positioned in his suprasternal notch, and the reflected energy is intercepted by a receiving transducer housed in the head of that probe.
The reflected energy contains information from which the systolic velocity of the blood flowing in the patient's ascending aorta can be calculated. From this parameter and the patient's aortic diameter the patient's cardiac output can be calculated as is explained in U.S. Pat. No. 4,509,526 which issued to Barnes et al on Apr. 9, 1985. U.S. Pat. No. 4,509,526 is assigned to the assignee of this application and is incorporated herein by reference.
Not easily met requirements are imposed on ultrasonic probes employed in the just-described technique for measuring cardiac output.
Ultrasonic probes as disclosed herein will typically be incorporated in equipment which is designed to monitor the cardiac output of a patient during a surgical procedure. The patient is commonly placed in a supine or reclining position during surgery and draped to expose the operating field to guard against infection. The operator of the cardiac output monitoring equipment, normally the anesthesiologist attending the operation, must be able to position and manipulate the ultrasonic probe from his position behind the head of the surgical patient.
During surgical procedures as described above, the head of the ultrasonic probe is visually obscured within the suprasternal notch of the patient and by the surgical drapes. The anesthesiologist or other operator of the cardiac output monitoring equipment will customarily also be monitoring a visual display as he manipulates the probe in order to achieve that orientation of the probe which will result in the ultrasonic beam being propagated in an optimum direction with respect to the patient's ascending aorta. Because of the visual obscuration, and the requirement that the operator be free to monitor a visual display, ultrasonic probes with which we are concerned must also be so designed that they can be positioned and manipulated primarily be feel.
It is furthermore required that the operator be comfortable while the ultrasonic probe is in use because surgical procedures can take several hours or more if the surgery is extensive.
Patient comfort is a requirement which should not be underestimated. If the patient moves while his cardiac output is being monitored, the transducer head of the ultrasonic probe may shift, causing erroneous data to be generated. Consequently, it is necessary that the patient remain reasonably still during the monitoring procedure; and this requires that the patient not be made uncomfortable by the probe, especially if he is conscious while it is being used.
The just-discussed combination of requirements are not met by the ultrasonic probes described in U.S. Pat. No. 4,582,066 issued Apr. 15, 1986, to Barnes et al. for ULTRASONIC TRANSDUCER PROBE because of the difficulty experienced in manipulating a probe with a straight handle from behind the patient's head. This makes it at least extremely hard to position and manipulate the probe with any degree of accuracy and can lead to both patient and operator discomfort.